The invention concerns a disconnecting device for a friction clutch of motor vehicles, including a slave cylinder which can be acted upon by means of a hydraulic fluid, and which contains a pressure housing attached to the front of a gear box housing and arranged concentrically around a drive shaft, whereby a guiding sleeve is arranged at a distance radially toward the drive shaft in a longitudinal bore in the pressure housing in which a ring piston is movably guided and which delimits a pressure chamber axially, whereby for sealing, the ring piston has a piston seal which is provided with sealing lips spread apart in the shape of a V.
Disconnecting devices generally of this type for use in connection with manual transmissions are known from numerous publications, for example U.S. Pat. No. 1,336,564. For sealing the pressure chamber, this publication discloses a ring piston seal with a symmetrical construction in connection with which the radially inner sealing lip as well as the radially outer sealing lip lie sealing on the guiding sleeve and bore wall of the pressure housing spread apart from each other in a V shape. Based on the differences in diameter between the sealing lips, sealing surfaces which deviate from each other result such that a contact force of the sealing lips similarly differs. From this it follows that with an axial movement of the ring piston on the radially outer sealing lip, greater forces of friction arise in comparison to the radially inner sealing lip. As a consequence of this, no consistent wear and tear pattern is established between the inner and outer sealing lip. The different stress upon the sealing lips in relation to each other can moreover lead to a disadvantageous extrusion of the outer sealing lip, or to a twisting of the seal, which brings about an impairment of function.
A radial seal with a U-shaped cross sectional profile is known from DE-U 88 01 765. The construction of this sealing ring provides a so-called connecting leg which is configured as a circular ring-shaped disk. Legs of identical length oriented in an axial direction are formed on the connecting leg on the inner and outer contour. The inner sealing leg moreover possess a lesser wall strength in comparison with the outer clamping leg. A sealing lip is assigned to both legs in the end region. Due to the large axial construction length and the great instability associated with this (especially of the inner sealing leg), this radial sealing ring is not suited for installation in a disconnecting device.